PURPOSE: To continuously process the information by adding the processes into the main and secondary processors to transmit the polling to call the process information out of a process input/output device together with the polling monitor processes added into both processors.

CONSTITUTION: A main system processor 11m, a secondary system processor 11s, a man-machine processor 11i, and a process input/output device 12 are connected with each other via a network 13 so that the information can be transmitted among them. Then the main system processor 11 transmits the polling to the network 13 to take the process information out of the device 12. The processor 11s monitors the polling at a fixed interval and then transmits another polling exactly equal to that transmitted by the processor 11 to the network 13 in the case no polling exists in the network 13 owing to the occurrence of a fault of the processor 11. As a result, the process information can be continuously taken out of the device 12.